Abstract
Fatal head-on crashes on two-lane rural highways can involve complex interactions among road users, vehicles, roadway conditions, roadside environments, and post-crash management. This study presents a systems-based comparative case study of two fatal heavy-vehicle head-on crashes on Iranian two-lane rural highways. The analysis integrated crash-sequence reconstruction, an adapted Haddon Matrix, and the Safe System Approach. The two cases involved a truck tractor colliding with two passenger cars and a truck colliding with a bus. Contributing factors were examined across pre-crash, crash, and post-crash phases and across four analytical domains: human factors, vehicle factors, road and environmental factors, and management or emergency response. The two crashes differed in their initiating mechanisms: unsafe overtaking and opposing-lane encroachment in one case, and tire failure followed by leftward truck deviation in the other. However, the case analyses showed that fatal outcomes were shaped by interactions among the initiating event, two-lane road configuration, absence of physical separation, roadway and roadside conditions, heavy-vehicle involvement, vehicle-condition issues, post-impact fire, and post-crash management considerations. The findings support a systems-based interpretation of fatal crash investigation evidence and highlight intervention opportunities at several points in the failure chain, including overtaking control, curve and sight-distance improvement, roadside hazard treatment, heavy-vehicle technical inspection, physical separation at priority locations, and strengthened emergency-response planning.